The hardest bit of your body is the enamel coating your teeth. But new analyses of fish fossils, as well as genetic analyses of a living fish species, suggest that this specialized material once served a very different function: to toughen some bones and scales of ancient fish. The findings bolster earlier suggestions that ancient fish had enamel-armored scales, and they point to a new scenario for exactly how the substance ended up on teeth.
Enamel—an almost pure layer of a mineral called hydroxyapatite—coats the teeth of almost all tetrapods (four-limbed creatures) and lobe-finned fish such as coelacanths. Most living fish do not produce it, but Per Ahlberg, a paleontologist at Uppsala University in Sweden, found an ancient exception. Well-preserved fossils of an ancient fish called Psaroepis romeri reveal that this 20-centimeter-long minipredator, which prowled the seas between 410 million and 415 million years ago, had enamel in its scales and its skull—but not its teeth, according to a paper by Ahlberg and colleagues in the 24 September issue of Nature.
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